Mobility management for high speed user equipment

ABSTRACT

The present invention relates to a method for efficiently supporting communication for vehicles in a next-generation wireless communication system and a device for the same. To this end, a user equipment (UE) receives signals from a network through a plurality of antenna units which are located in dispersed locations of the UE, determines, through a central unit thereof, whether a mobility related event of the UE has occurred through the signals received through the plurality of antenna units and transmits an event occurrence report to the network when the mobility related event of the UE has occurred, wherein whether the mobility related event of the UE has occurred is determined in consideration of receive (Rx) power of the signals received through the plurality of antenna units and a ray distribution between the network and the UE.

TECHNICAL FIELD

The following description relates to a method and apparatus forefficiently managing mobility of high speed user equipment (UE) in anext-generation wireless communication system and, particularly, to amethod and apparatus for efficiently providing mobility management to aUE for vehicles to which a distributed antenna array is applied.

BACKGROUND ART

In the conventional mobile communication system for mainly servingpersonal mobile communication devices, there is an inverse proportionalrelationship between the speed of the UE and required data rate andquality of service (QoS). So, the conventional communication system isconfigured to provide high data rate/QoS for low speed UE, and toprovide reliable service without radio link failure for the high speedUE even if the data rate/QoS is somewhat low.

In the next generation communication system, there is a need for highdata rate/QoS for the high speed UE, since the scope of the requiredservice increase. For example, the users in the vehicle or publictransportation would like to enjoy multi-media service during the driveon a highway. Also, users want to enjoy multi-media service more whilethe speed of the vehicle is high.

This is a new model which does not exist in conventional wirelesscommunication service models. To support this, mobile communicationnetworks need to be enhanced to a revolutionary level or a new systemcapable of realizing the new model without affecting networkinfrastructures needs to be designed.

In next-generation mobile communication systems, V2X(Vehicle-to-Infrastructure/Vehicle/Nomadic) communication technology forsupporting efficient vehicle communion is under discussion. V2Xcommunication includes communication between a vehicle andinfrastructure (V2I) and communication between vehicles (V2V).

When a large antenna array is provided to the outside of a vehicle inorder to provide a high quality communication service to high speedvehicles, aesthetic/aerodynamic problems are generated and thus researchinto vehicle antennas for replacing the large antenna array is required.

In addition, when an event that a signal of a serving cell decreasesbelow a specific threshold value compared to neighboring cells in orderto manage UE mobility occurs, a UE reports occurrence of the event tothe serving cell for UE mobility management in a conventionaltechnology. However, efficiency of application of this technology tovehicular communication needs to be examined.

DISCLOSURE Technical Problem

An efficient UE mobility management method and a UE configurationtherefor in order to support high-quality vehicular communicationservices will be described.

Technical Solution

To accomplish the aforementioned object, one aspect of the presentinvention proposes a method by which a user equipment (UE) performsreporting for mobility management in a wireless communication system,including: receiving, from a network, signals through a plurality ofantenna units of the UE located at distributed positions; determining,by a central unit of the UE, whether a mobility related event of the UEhas occurred through the signals received through the plurality ofantenna units; and transmitting an event occurrence report to thenetwork when the mobility related event of the UE has occurred, whereinwhether the mobility related event of the UE has occurred is determinedin consideration of receive (Rx) power of the signals received throughthe plurality of antenna units and a ray distribution between thenetwork and the UE.

Here, the signals received from the network may be signals transmittedthrough a plurality of antennas from the network, and the raydistribution between the network and the UE may be considered usingangles of departure (AoD) of the signals transmitted through theplurality of antennas.

Here, it may be determined that link reliability with respect to thespecific network device is proportional to the number of rays/beamsreceived through the plurality of antenna units from a specific networkdevice of the network and magnitude of AoD differences between therays/beams.

Here, the number of received rays/beams may be regarded as the number ofbeams having receive power equal to or higher than a predeterminedreference level among all received rays/beams.

The Rx power of the signals received through the plurality of antennaunits may be considered through at least one of Rx power or quality of asignal received by each antenna unit from each network device of thenetwork, Rx power or quality of signals received by all of the pluralityof antenna units from each network device of the network, Rx power orquality of each received signal preferred by each antenna unit amongsignals received from each network device of the network, and Rx poweror quality of all received signals preferred by each antenna unit amongsignals received from each network device of the network.

In addition, different measurement durations may be set for respectiveparameters considered for determining whether the mobility related eventof the UE has occurred.

Further, whether the mobility related event of the UE has occurred maybe determined by independently determining whether a plurality ofconditions is satisfied or may be determined in such a manner that, whena first condition among a plurality of conditions is satisfied, whethera second condition following a first condition is satisfied isdetermined.

Further, the event occurrence report may include information about raydirectivity from a specific network device of the network.

In another aspect of the present invention to accomplish theaforementioned object, a UE for which mobility management is supportedin a wireless communication system includes: a plurality of antennaunits located at distributed positions; and a central unit connected tothe plurality of antenna units and configured to determine whether amobility related event of the UE has occurred through signals receivedthrough the plurality of antenna units, wherein the central unitdetermines whether the mobility related event of the UE has occurred inconsideration of Rx power of the signals received through the pluralityof antenna units and a ray distribution between a network and the UE.

Here, the plurality of antenna units may be configured to receivesignals transmitted through a plurality of antennas from the network,and the central unit may consider the ray distribution between thenetwork and the UE using angles of departure of the signals transmittedthrough the plurality of antennas.

The central unit may determine that link reliability with respect to thespecific network device is proportional to the number of rays/beamsreceived through the plurality of antenna units from a specific networkdevice of the network and magnitude of AoD differences between therays/beams. Here, the number of received rays/beams may be regarded asthe number of beams having receive power equal to or higher than apredetermined reference level among all received rays/beams.

The central unit may consider the Rx power of the signals receivedthrough the plurality of antenna units through at least one of Rx poweror quality of a signal received by each antenna unit from each networkdevice of the network, Rx power or quality of signals received by all ofthe plurality of antenna units from each network device of the network,Rx power or quality of each received signal preferred by each antennaunit among signals received from each network device of the network, andRx power or quality of all received signals preferred by each antennaunit among signals received from each network device of the network.

The central unit may set different measurement durations for respectiveparameters considered for determining whether the mobility related eventof the UE has occurred.

Advantageous Effects

An efficient UE mobility management method and a UE configurationtherefor in order to support high-quality vehicular communicationservices will be described.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a structure of conventional shark antenna system forvehicular communication.

FIG. 2 shows a concept of in-vehicle DAS system implemented into a car.

FIG. 3 schematically illustrates the reason why a distributed antennasystem is more suitable to prevent link failure than conventionalsystems when ray-block is generated due to vehicle movement.

FIG. 4 illustrates conventional radio resource monitoring (RRM) foreNB/cell selection.

FIG. 5 illustrates problems of a conventional Rx power based cellselection method and a cell selection method proposed in an embodimentof the present invention.

FIGS. 6 and 7 illustrate a method of triggering an event inconsideration of ray diversity as proposed in an embodiment of thepresent invention.

FIG. 8 illustrates a method of triggering a handover event inconsideration of ray diversity.

FIGS. 9 and 10 illustrate a method of selecting and processing apreferred beam for each antenna unit in an embodiment of the presentinvention and FIG. 11 illustrates a method of measuring RxP withoutconsidering precoding gain as in the conventional method.

FIG. 12 illustrates a method of determining beam diversity using anangle of arrival (AoA) per antenna unit in a second aspect of thepresent invention.

FIG. 13 illustrates a method of measuring Rx quality distribution forAoA according to the second aspect of the present invention.

FIGS. 14 and 15 illustrate measurement examples considering both anangle of departure (AoD) and AoA per ray.

FIG. 16 illustrates a method of adjusting a link reliabilitydetermination algorithm and a handover determination algorithmadaptively to situation through enabling or disabling signaling for eachsub-tree.

FIG. 17 illustrates an apparatus for performing the above-describedoperations.

MODE FOR INVENTION

Reference will now be made in detail to the exemplary embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The detailed description, which will be given below withreference to the accompanying drawings, is intended to explain exemplaryembodiments of the present invention, rather than to show the onlyembodiments that can be implemented according to the invention.

The following detailed description includes specific details in order toprovide a thorough understanding of the present invention. However, itwill be apparent to those skilled in the art that the present inventionmay be practiced without such specific details. In some instances, knownstructures and devices are omitted or are shown in block diagram form,focusing on important features of the structures and devices, so as notto obscure the concept of the present invention.

As described above, the following description relates to a method andapparatus for efficiently providing mobility management to a UE forvehicles to which a distributed antenna array is applied in anext-generation wireless communication system.

Distributed Antenna Array

As described above, a vehicular MIMO system in which a large sizeantenna array is installed in a vehicle such that a high-quality servicecan be provided to the vehicle through a large array gain even when thevehicle moves at a high speed, and a central unit of the vehicle relaysreceived data to a passenger is considered in order to provide efficientvehicular communication.

When the large size antenna array is installed outside of the vehicleand radio communication is relayed between a base station and apassenger in the vehicle through the large size antenna array,communication performance deterioration due to penetration loss havingan average value of about 20 dB can be prevented, a large array gain canbe secured by using a larger number of Rx antennas than a personalmobile communication device, and a distance between Rx antennas can beeasily secured to easily obtain Rx diversity.

According to the aforementioned features, vehicular MIMO can providecommunication services superior to personal mobile devices withoutadditional infrastructure investment

Despite the above-described advantage, there is no example in which alarge antenna array is installed in a vehicle. Since a vehicle is aconsiderably expensive apparatus compared to personal mobilecommunication devices, is difficult to enhance and upgrade, and needs tosatisfy many requirements such as design concept, aerodynamic structureand the like in addition to communication performance, it is not easy toinstall the large antenna array which aesthetically/aerodynamicallylimits vehicle design. Vehicle manufacturers use a combined antennahaving lower performance than a single antenna in order to eliminatevisual inconvenience due to existing antennas.

FIG. 1 shows a structure of conventional shark antenna system forvehicular communication.

In FIG. 1, the shark antenna includes combined structure for 4 or moredifferent band/services in one antenna.

However, this shark antenna is a combined antenna having lowerperformance than a single antenna, which is used by vehiclemanufacturers in order to eliminate visual inconvenience due to existingantennas, as described above, and thus is insufficient to providehigh-quality vehicular communication.

Accordingly, one aspect of the present invention considers installationof a distributed antenna array system for realizing an arrayed antennasystem through multiple arrays instead of a single array in a vehicle inorder to overcome spatial restriction of a large array antenna.

FIG. 2 shows a concept of an in-vehicle DAS system installed in a car.

Antennas having various forms and emission patterns depending oninstallation positions are disposed at distributed positions, and acentral unit for controlling transmission and reception of signals in anintegrated manner through the antennas may be installed as shown in FIG.2. According to this configuration, a reception (Rx) diversity gain canbe maximized using the antenna array and a situation in which wirelessconnection between a base station and a vehicle receiver is interruptedduring high-speed movement causing abrupt communication environmentchange can be prevented through cooperative reception of antennas havingdifferent emission patterns.

An antenna unit which is disposed in a distributed manner in a vehicleas illustrated in FIG. 2 may be called a “distributed unit” (DU) andwill be referred to as “antenna sub-array” or “antenna unit” in thefollowing description.

FIG. 3 schematically illustrates the reason why a distributed antennasystem is more suitable to prevent link failure than conventionalsystems when ray-block is generated due to vehicle movement.

In vehicular communication, when an obstacle such as a truck moves atone side of a vehicle at a speed similar to that of the vehicle and thusa beam is received only in the direction in which the truck moves,communication failure may occur for a considerable time.

However, when the aforementioned distributed antenna system is appliedas shown in FIG. 3, a beam received from a network device may havevarious paths and thus a problem that an obstacle moving at one side ofa vehicle directly affects communication can be mitigated.

In FIG. 3, a network device which transmits signals to a UE for vehiclesmay be a conventional eNB or a roadside device installed for vehicularcommunication. In addition, signals from the network device may bedirectly received by the UE for vehicles or reflected by a specificreflector and received.

Problem of Current Cell Selection Method

As described above, the distributed array antenna is an array solutionsuitable for mobile communication for vehicles which can enhance Rxpower gain by realizing a large array antenna and overcome communicationperformance deterioration and link failure during ray-block. However, toobtain an actual gain through the aforementioned antenna structure in amobile communication system, an access control method appropriate forthe antenna structure needs to be applied. A conventional access controlmethod which mainly uses a personal mobile communication device using asingle antenna array is an Rx power based access control method whichrelatively compares Rx powers of cell search reference signalstransmitted from eNBs to select an eNB most suitable to provide servicesto each UE and does not provide abundant rays required to preventperformance deterioration due to ray-block and a function of comparingRx diversity gains.

FIG. 4 illustrates a conventional radio resource monitoring (RRM) methodfor eNB/cell selection.

To request eNB/cell change from an eNB to which a UE is currentlyconnected, an “event” indicating that eNB/cell change may be neededneeds to be triggered. The event is triggered 1) when Rx power of a cellsearch reference signal of a serving cell decreases below an appropriatevalue and thus access point change to another eNB/cell needs to beconsidered, 2) when “a cell search reference signal of a cell other thanthe serving cell is received with higher power than the cell searchreference signal of the serving cell for a predetermined time” and thusit is determined that an eNB/cell, which is more suitable to be used asan access point than the current serving cell, exists, or 3) when theaforementioned two situations simultaneously/sequentially occur.

When the event occurs, a network or a serving cell eNB may request thatthe UE measure and report more detailed channel state, perform/instructserving cell change, or determine that the current serving cell ismaintained in consideration of various network factors that are notrecognized by the UE, such as traffic balancing.

Proposed Cell Selection Method

FIG. 5 illustrates a problem of a conventional Rx power based cellselection method and a cell selection method proposed in an embodimentof the present invention.

In FIG. 5, although a vehicle is close to a first cell c0 and thusmeasures and reports high Rx power for a cell search reference signal ofc0, only one ray exists between the vehicle and c0 so that link failuremay occur when an object that obstructs the ray appears.

A second cell c1 a relatively longer distance from the vehicle cannotprovide high Rx power to the vehicle but can support communicationthrough various “rays” and thus can stably secure a link even when acommunication blocker appears. When the vehicle moves at a high speed,cell selection in consideration of the aforementioned “ray distribution”information needs to be performed.

Accordingly, the present invention defines a new event for determininglink stability between a cell and a terminal (vehicle) in considerationof ray distribution and triggering an RRM event on the basis of the linkstability. The new event defined in the present embodiment is applicableto various access controls such as cell selection, reselection, handoverand neighbor cell search request.

In the following description, it is assumed that “terminal” and “UE”refer to a user device accompanying high-speed movement such asvehicles, but they are not necessarily limited to vehicles. In addition,a network device may be various devices such as an existing eNB and celland may be a roadside unit installed on the roadside according to newlyconstructed infrastructure.

To calculate “ray distribution” information, it is desirable that a UEreceive a cell search reference signal transmitted from a network devicethrough multiple ports or precoded and transmitted with directivity.Accordingly, in a first aspect of the present invention, “raydistribution” information, particularly, an angle of departure (AoD) andRx power/gain estimated when precoding/beamforming is performed can bemeasured through a method of determining a precoder or beamformer formsuitable (preferred) to be used at a transmitter when a reference signaltransmitted through multiple antenna ports is received as describedabove.

However, the network device may not have a plurality of transmit (Tx)antenna ports as described above. Accordingly, another aspect (secondaspect) of the present invention proposes a method of measuring an angleof arrival (AoA) of a reference signal per sub-array and acquiring “raydistribution” information, particularly, information about thepossibility that rays are blocked due to an obstacle close to a UE, fromthe AoA per sub-array when the network device transmits referencesignals through a single Tx antenna.

The first aspect and the second aspect of the present invention canrespectively correspond to a case using AoD and a case using AoA when“ray distribution” information is calculated depending on whether thenetwork device uses multiple antenna ports or a single antenna port.However, the two aspects can be simultaneously generated in onecommunication system according to situation, and thus techniquesaccording to the aspects described below may be combined.

Various embodiments of a UE mobility management method for efficientvehicular communication will be described in detail in terms of theaforementioned two aspects on the basis of the above description.

Embodiment 1

Embodiment 1 of the present invention proposes a method by which a UEdetermines link reliability per cell in consideration of AoD of raysbetween an eNB/cell and a sub-array and triggers an RRM event using thelink reliability or feeds back related information.

In the following description, an RRM event may be as follows.

(1) A UE determines that link reliability of a serving cell is lowerthan an appropriate level and reports the link reliability to aneNB/cell or

(2) the UE determines that there is another cell which has higher linkreliability than the current serving cell and thus is more suitable asan access point

The RRM event refers to a measurement parameter necessary to determine acurrent radio resource state or change, a process for determining thataccess control needs to be performed using the measurement parameter ordetermining that link state change needs to be reported to an eNB/cell,and a method of reporting the event or measurement parameter. In thepresent embodiment, a method of newly defining the event correspondingto (1) and a method of newly defining the event corresponding to (2)using the same are proposed.

When a UE reports the occurrence of a new event proposed in the presentembodiment to an eNB/cell, the UE may report an indicator indicating theoccurrence of the event or directly report a measurement parameter usedto determine the occurrence of the event to the eNB/cell. In this case,it may be desirable to report a new parameter which is not used inconventional event reporting to the eNB/cell.

In the first aspect of the present invention, that is, when atransmitter uses multiple antennas, the aforementioned additional reportparameter may take a form of AoD, precoder matrix index, AoD indicator,angular spread of transmit rays, preferred Tx beam indexes or the like.

In the second aspect of the present invention, that is, when atransmitter uses a single antenna, the aforementioned additional reportparameter may take a form of AoA, AoA representative value, codebookbased AoA indicator, angular spread of received rays, best N rays AoAindex(es) or the like.

In addition, the parameter may include spatial characteristics betweenthe eNB/cell and the UE, particularly, information about ray/beamdirectivity.

FIGS. 6 and 7 illustrate a method of triggering an event inconsideration of ray diversity as proposed in an embodiment of thepresent invention and FIG. 8 illustrates a method of triggering ahandover event in consideration of ray diversity.

As illustrated in FIGS. 6 and 7, angle information about ray/Tx beam andinformation about Rx power (propagation gain and processing gain) may beindependently used to determine link reliability (FIG. 6) or used todetermine link reliability in consideration of correlation therebetween(FIG. 7). Details will be described through the following embodiment.

As shown in FIG. 8, whether an event is triggered can be determinedthrough combination of measurement values of two or more parameters.Details will be described through the following embodiment.

In the first aspect of the present invention, that is, in the case ofreference signal transmission through multiple antennas, a UE mayperform “preferred beam searching” for a cell search reference signalupon reception of the cell search reference signal. Through thisoperation, the UE can 1) distinguish a ray having a higher propagationgain and a higher estimated beamforming gain than other rays from otherrays and 2) acquire a transmitter precoder form suitable for downlinkreception, that is, AoD information of a beam through the ray.

FIGS. 9 and 10 illustrate a method of selecting and processing apreferred beam for each antenna unit in an embodiment of the presentinvention and FIG. 11 illustrates a method of measuring RxP withoutconsidering a precoding gain as in the conventional method.

The present embodiment proposes a method of determining link reliabilityper cell using all or some measurement values obtained through themethods illustrated in FIGS. 9 to 11. Operation of a receiver asillustrated in FIGS. 9 and 10 will be described in more detail.

1) The receiver estimates a MIMO channel corresponding to an array orsub-array.

2) A set of Tx beams (AoD, PMI, etc.) having gains equal to or higherthan a fixed value is selected from the MIMO channel estimated inprocess 1).

3) The Tx beam set selected in process 2) and the gain of each Tx beamare analyzed to determine link reliability of the correspondingcell/eNB.

When the number of Tx beams selected to determine link reliability inprocess 3) is large and a difference between AoD values of Tx beams islarge, the cell/eNB can be determined to have high link reliability(e.g., c1 in FIG. 5). On the contrary, when the number of selected Txbeams is small or a difference between AoD values of the correspondingbeams is not large, the cell/eNB can be determined to have low linkreliability (e.g., c0 in FIG. 5).

In addition to the above-described method, when a plurality of cellsearch RSs is transmitted in the form of precoded RSs (beamformed RSs),Rx quality distribution for a beam index (or AoD) similar to FIGS. 9 and10 can be measured by measuring Rx quality for each cell search RS.

In the second aspect of the present invention, that is, in the case ofreference signal transmission through a single antenna, a UE measures anangle of arrival (AoA) for a cell search reference signal upon receptionof the cell search reference signal. Through this operation, the UEcan 1) distinguish a ray having higher propagation gain and higherestimated Rx beamforming gain than other rays from other rays and 2)acquire AoA information and estimated gain information during downlinkreception through the ray.

FIG. 12 illustrates a method of determining beam diversity using AoA perantenna unit in the second aspect of the present invention.

The second aspect of the present invention proposes a method ofdetermining link reliability per cell using all or some measurementvalues obtained through FIG. 11 or 12. Operation of a receiver asillustrated in FIG. 12 will be described in more detail.

1) The receiver estimates a MIMO channel corresponding to an array orsub-array.

2) A set of Rx beams (AoA) having gains equal to or higher than a fixedvalue is selected from the MIMO channel estimated in process 1).

3) The Rx beam set selected in process 2) and the gain of each Rx beamare analyzed to determine link reliability of the correspondingcell/eNB.

When the number of Rx beams selected to determine link reliability inprocess 3) is large and a difference between AoA values of Rx beams islarge, the cell/eNB can be determined to have high link reliability(e.g., c1 in FIG. 5). On the contrary, when the number of selected Rxbeams is small or a difference between AoA values of the correspondingbeams is not large, the cell/eNB can be determined to have low linkreliability (e.g., c0 in FIG. 5).

The aforementioned method is applicable to both a case in which a cellsearch RS is transmitted through a single port and a case in which thecell search RS is transmitted through multiple ports and can be appliedirrespective of cell search RS transmission form such as transmission ofmultiple RSs in the form of precoded RSs (beamformed RSs). In addition,in AoA measurement, an AoA can be measured in various manners such asmeasurement of AoA per sub-array and measurement of AoA per RS.According to the aforementioned operation, Rx quality distribution forAoA as shown in FIG. 13 can be measured.

FIG. 13 illustrates a method of measuring Rx quality distribution forAoA according to the second aspect of the present invention.

Specifically, FIG. 13 a) shows Rx power and AoA distribution for each ofa plurality of Rx sub-arrays and FIG. 13 b) shows Rx power and AoAdistribution per sub-array and per Tx port/beam.

Embodiment 2

Embodiment 2 is a sub-embodiment of the above-described embodiment 1 andproposes additional consideration of one or more of the followingmeasurement values in determination of link reliability per cell inconsideration of AoD and intensity distribution of rays between aneNB/cell and sub-arrays according to the first aspect of the presentinvention.

A. Rx power/quality per sub-array for each eNB/cell

B. Rx power/quality of the entire array

C. Rx power/quality of each preferred Tx beam of each sub-array

D. Rx power/quality of each preferred Tx beam of all sub-arrays

In the second aspect of the present invention, “Tx beam” may be replacedby “Rx beam” in the additionally considered parameters A to D.

Example 1

Rx power and AoD with respect to a preferred Tx beam of each sub-arrayare considered (A and C values are used).

1) A UE calculates a sub-array which satisfies RxP_n>TH_P amongsub-arrays.

2) In the first aspect using multiple antennas, the UE calculates AoDvalues for L rays or beams which guarantee the largest gain for thesub-array or calculates rays or beams which satisfy gain >TH_P0 amongrays or beams of the sub-array. In the second aspect using a singleantenna, the UE may use AoA instead of AoD.

3) A first condition of a cell which provides a stable link is definedas a condition that the number of rays/beams which satisfy theaforementioned conditions is equal to or greater than TH_N or acondition that the number of sub-arrays which satisfy the condition 1 isequal to or greater than TN_N.

4) Only for sub-arrays which satisfy the first condition (sub-arrays inwhich the number of rays/beams satisfying the condition 2 is equal to orgreater than TH_N, or sub-arrays which satisfy the condition 1), the UEcalculates AoD values or AoA values of the rays/beams. A parameter(e.g., maximum value-minimum value, or a variance of AoD/AoA values)which can indicate a distribution of the AoD or AoA values is defined,and when the parameter is equal to or greater than TH_D, it isdetermined that a second condition for determining a cell which providesa stable link is satisfied.

5) The UE determines a cell which satisfies the aforementioned twoconditions as a cell which provides a stable link, and when a servingcell does not satisfy any one of the two conditions, determines that“link reliability reduction event” has occurred and reports occurrenceof the link reliability reduction event to the eNB/cell/serving cell.

The same algorithm is applicable to a case in which there is onesub-array, that is, the entire array is implemented as a single array.

Example 2

Rx power and AoD (AoA) of the entire array are considered (B and Dvalues are used)

1) The UE measures Rx power of a cell search reference signal for theentire array, and when the measured value is equal to or greater thanTH_P, determines that the first condition for determining a cellproviding a stable link is satisfied.

2) The UE calculates AoD (AoA) values for L rays or beams whichguarantee the largest gain among all rays/beams or calculates rays orbeams which satisfy precoded Rx power >TH_P0 among all rays/beams.

3) The UE calculates AoD (AoA) values of the calculated rays/beams. Aparameter (e.g., maximum value-minimum value, or a variance of AoD (AoA)values) which can indicate a distribution of the AoD values is defined,and when the parameter is equal to or greater than TH_D, it isdetermined that the second condition for determining a cell whichprovides a stable link is satisfied.

4) The UE determines a cell which satisfies the aforementioned twoconditions as a cell which provides a stable link, and when the servingcell does not satisfy any one of the two conditions, determines that“link reliability reduction event” has occurred and reports occurrenceof the link reliability reduction event to the eNB/cell/serving cell.

Example 3

In the second aspect of the present invention, Rx powers and AoAdistributions of different rays/beams for each sub-array are considered(C value is used)

1) Depending on RxP_nm, which is Rx power per ray/beam of each array,the UE

1-1) selects L largest gain rays/beams per sub-array,

1-2) selects L_n rays/beams per sub-array, which make a precoded RxP sumof the largest gain rays/beams per sub-array become TH_P or more, or

1-3) calculates rays/beams which satisfy RxP_nm per sub-array >TH_P.

2) The UE

2-1) calculates the number of sub-arrays which satisfy the precoded RxPsum of the L rays/beams per sub-array >TH_P0 or the number of sub-arrayswhich satisfy minimum precoded Rx power of the L rays/beams persub-array >TH_P0 upon selection of the L rays/beams per sub-arrayaccording to 1-1, and then determines that the first condition fordetermining a cell providing a stable link is satisfied when the numberof sub-arrays is equal to or greater than TH_N,

2-2) determines that the first condition for determining a cellproviding a stable link is satisfied if the number sub-arrays whichsatisfy L_n<TH_N0 is equal to or greater than TH_N upon selection of theL_n rays/beams per sub-array according to 1-2, and

2-3) determines that the first condition for determining a cellproviding a stable link is satisfied if the number sub-arrays in whichthe number of rays/beams per sub-array is equal to or greater than TH_N0is equal to or greater than TH_N when 1-3 is applied.

3) When the first condition is satisfied, the UE calculates AoA valuesfor rays/beams which correspond to the sub-arrays satisfying the firstcondition and are calculated for each the aforementioned cases. Aparameter (e.g., maximum value-minimum value, or a variance of AoAvalues) which can indicate a distribution of the AoA values is defined,and when the parameter is equal to or greater than TH_A, it isdetermined that the second condition for determining a cell whichprovides a stable link is satisfied.

3-1) For example, when 1-1 and 2-1 are applied, AoA values arecalculated for L rays/beams of each sub-array satisfying the conditionof 2-1. A case in which 1-2 and 2-2 are applied and a case in which 1-3and 2-3 are applied can be naturally interpreted and thus detaileddescription thereof is omitted.

4) The UE determines a cell which satisfies the aforementioned twoconditions as a cell which provides a stable link, and when a servingcell does not satisfy any one of the two conditions, determines that“link reliability reduction event” has occurred and reports occurrenceof the link reliability reduction event to the eNB/cell/serving cell.

Example 4

Power and AoD (AoA) distribution for each preferred Tx beam of theentire array are considered (D value is used)

1) The UE selects L largest gain rays/beams or calculates rays/beamswhich satisfy RxP_nm>TH_P depending on RxP_nm which is precoded Rx powerof each ray/beam of each sub-array.

2) The UE determines that the first condition for determining a cellproviding a stable link is satisfied when the precoded Rx power sum ofthe L rays/beams is equal to or greater than TH_P1 or the number ofrays/beams which satisfy RxP_nm>TH_P0 is equal to or greater than TH_N.

3) The UE calculates AoD (AoA) values of the aforementioned rays/beams.A parameter (e.g., maximum value-minimum value, or a variance of AoD(AoA) values) which can indicate a distribution of the AoD (AoA) valuesis defined, and when the parameter is equal to or greater than TH_D, itis determined that the second condition for determining a cell whichprovides a stable link is satisfied.

4) The UE determines a cell which satisfies the aforementioned twoconditions as a cell which provides a stable link, and when a servingcell does not satisfy any one of the two conditions, determines that a“link reliability reduction event” has occurred and reports occurrenceof the link reliability reduction event to the eNB/cell/serving cell.

Example 5

Another method considering Rx powers and AoD (AoA) distributions ofdifferent rays/beams for the entire array (D value is used)

1) The UE arranges all rays/beams in order of RxP_nm levels. This isreferred to as RxP_0, RxP_1, . . . for convenience of description.

2) The UE selects 2-1) K rays/beams which satisfy RxP_0+RxP_1_+ . . .+RxP_k>TH_P or 2-2) L largest gain rays/beams from the aforementionedrays/beams.

3) When K satisfying the condition of 2-1 is equal to or less than TH_N,the precoded Rx power sum of the L rays/beams is equal to or greaterthan TH_P or minimum precoded Rx power of the L rays/beams is equal toor greater than TH_P0, it is determined that the first condition fordetermining a cell providing a stable link is satisfied.

4) The UE calculates AoD (AoA) values for the min(K, TH_N) or Lrays/beams. A parameter (e.g., maximum value-minimum value, or avariance of AoD (AoA) values) which can indicate a distribution of theAoD (AoA) values is defined, and when the parameter is equal to orgreater than TH_D, it is determined that the second condition fordetermining a cell which provides a stable link is satisfied.

The UE determines a cell which satisfies the aforementioned twoconditions as a cell which provides a stable link, and when a servingcell does not satisfy any one of the two conditions, determines that“link reliability reduction event” has occurred and reports occurrenceof the link reliability reduction event to the eNB/cell/serving cell.

Example 6

Rx powers and AoD distribution of different rays/beams for eachsub-array are considered (C value is used)

1) The UE selects 1-1) L largest gain rays/beams or 1-2) L_n rays/beamsper sub-array, which make a precoded RxP sum of the largest gainrays/beams per sub-array become TH_P or more, for each sub-arraydepending on RxP_nm which is Rx power per ray/beam of each sub-array.Otherwise, the UE calculates rays/beams which satisfy RxP_nm persub-array >TH_P.

2) The UE

2-1) calculates the number of sub-arrays which satisfy the precoded RxPsum of the L rays/beams per sub-array >TH_P0 or the number of sub-arrayswhich satisfy minimum precoded Rx power of the L rays/beams persub-array >TH_P0 upon selection of the L rays/beams per sub-arrayaccording to 1-1, and then determines that the first condition fordetermining a cell providing a stable link is satisfied when the numberof sub-arrays is equal to or greater than TH_N,

2-2) determines that the first condition for determining a cellproviding a stable link is satisfied if the number sub-arrays whichsatisfy L_n<TH_N0 is equal to or greater than TH_N upon selection of theL_n rays/beams per sub-array according to 1-2, and 2-3) determines thatthe first condition for determining a cell providing a stable link issatisfied if the number sub-arrays in which the number of rays/beams persub-array is equal to or greater than TH_N0 is equal to or greater thanTH_N when 1-3 is applied.

3) When the first condition is satisfied, the UE calculates AoD valuesfor rays/beams which correspond to the sub-arrays satisfying the firstcondition and are calculated for each of the aforementioned cases. Aparameter (e.g., maximum value-minimum value, or a variance of AoDvalues) which can indicate a distribution of the AoD values is defined,and when the parameter is equal to or greater than TH_D, it isdetermined that the second condition for determining a cell whichprovides a stable link is satisfied.

3-1) For example, when 1-1 and 2-1 are applied, AoD values arecalculated for L rays/beams of each sub-array satisfying the conditionof 2-1. A case in which 1-2 and 2-2 are applied and a case in which 1-3and 2-3 are applied can be naturally interpreted and thus detaileddescription thereof is omitted.

4) The UE determines a cell which satisfies the aforementioned twoconditions as a cell which provides a stable link, and when a servingcell does not satisfy any one of the two conditions, determines that“link reliability reduction event” has occurred and reports occurrenceof the link reliability reduction event to the eNB/cell/serving cell.

Example 7

The link reliability determination methods proposed in theabove-described examples are performed for a plurality of eNBs/cells andthen whether an RRM event is triggered is determined on the basis of theresult

The above-described examples of an RRM event follow embodiment 1.Examples of applying the aforementioned methods to handover among RRMevents will be described. Even when a link with a serving cell is stableand communication quality beyond requirements is guaranteed, handovermay be necessary to support better services. Although a conventionalmethod considers only Rx power of a cell search reference signal andthus can easily define a handover algorithm in a manner of selecting acell having higher Rx power as a serving cell, a more complicatedalgorithm needs to be defined when both Rx power and link stabilityshould be considered.

To this end, in determination of link reliability per eNB/cell, a UEdefines a plurality of parameters indicating link reliability,determines superiority between eNBs/cells for each parameter, and thencompares link reliabilities or link suitability between eNBs/cells.

FIG. 8 illustrates a case in which two parameters are used to indicatelink reliability.

Embodiment 3

Both AoD and AoA of each ray are considered in definition of RRM eventtrigger conditions using link reliability.

Checking link reliability in consideration of AoA of Rx beams is amethod of considering only some information which can be easilyrecognized by a UE from among information about channel directivity. Ifthe UE has sufficient modem capability, the UE can recognize moreaccurate information about channels and determine link reliability withhigh reliability on the basis of the information.

FIGS. 14 and 15 illustrate an example of measurement considering bothAoD and AoA of each ray.

Tx beams or AoD which guarantee sufficient Rx power or propagation gainmay be calculated and, when transmitter beamforming is performeddepending on the AoD, AoA of each beam may be calculated. Here, thenumber of calculated Tx beams may be different for sub-arrays, UEs(vehicles) and target eNBs/cells.

Example 8

AoA per sub-array in the above-described examples is replaced by AoA perTx beam and link reliability is determined.

Operation per “sub-array” in all examples with respect to embodiment 2may be switched to operation per “Tx beam” and the link reliabilitydetermination process may be performed. For example, when “example 1” isswitched to a method of considering AoD (AoA) per Tx beam,

1) The UE calculates Tx beams which satisfy RxP_nm>TH_P among Tx beamsof each sub-array.

2) The UE calculates AoD (AoA) values for L Rx beams which guarantee thelargest gain or calculates Rx beams which satisfy RxP_nm_pq>TH_P0 amongRx beams corresponding to the Tx beams, for each Tx beam.

3) The first condition of a cell which provides a stable link is definedas a condition that the number of all Rx beams which satisfy theaforementioned conditions is equal to or greater than TH_N or acondition that the number of Tx beams which satisfy condition 1 is equalto or greater than TH_N.

4) The UE calculates AoD (AoA) values of the Rx beams only for Tx beamswhich satisfy the first condition (Tx beams for which the number of Rxbeams satisfying condition 2 is equal to or greater than TH_N or Txbeams which satisfy condition 1). A parameter (e.g., maximumvalue-minimum value, or a variance of AoD (AoA) values) which canindicate a distribution of the AoD (AoA) values is defined, and when theparameter is equal to or greater than TH_D, it is determined that thesecond condition for determining a cell which provides a stable link issatisfied.

5) The UE determines a cell which satisfies the aforementioned twoconditions as a cell which provides a stable link, and when a servingcell does not satisfy any one of the two conditions, determines that a“link reliability reduction event” has occurred and reports occurrenceof the link reliability reduction event to the eNB/cell/serving cell.

Example 9

In the above-described examples, after determination of a sub-conditionfor Rx power for the entire array or each sub-array, a sub-condition forRx power per Tx beam of each sub-array may be determined. Then, linkreliability is determined in consideration of AoD (AoA) per Rx beam.

For example, when this method is applied to example 1,

1) The UE calculates sub-arrays which satisfy RxP_n>TH_P.

1-1) The UE calculates Tx beams which satisfy RxP_nm>TH_P0 among Txbeams of each sub-array satisfying the aforementioned condition.

2) For the Tx beams per sub-array, the UE calculates AoD (AoA) valuesfor L rays or Rx beams which guarantee the largest gain or calculatesrays or Rx beams which satisfy gain >TH_P1 among rays or Rx beams forthe Tx beams per sub-array.

3) The first condition of a cell which provides a stable link is definedas a condition that the number of rays/Rx beams which satisfy theaforementioned conditions is equal to or greater than TH_N or acondition that the number of sub-arrays which satisfy condition 1 isequal to or greater than TH_N.

3-1) Otherwise, the number of Tx beams which satisfy condition 1-1 isdefined as TH_N0 or more. Otherwise, a case in which two or more of theabove-described three conditions are satisfied is defined.

4) The UE calculates AoA values of the aforementioned rays/Rx beams onlyfor Tx beams which satisfy the first condition. A parameter (e.g.,maximum value-minimum value, or a variance of AoD (AoA) values) whichcan indicate a distribution of the AoA values is defined, and when theparameter is equal to or greater than TH_A, it is determined that thesecond condition for determining a cell which provides a stable link issatisfied.

5) The UE determines a cell which satisfies the aforementioned twoconditions as a cell which provides a stable link, and when a servingcell does not satisfy any one of the two conditions, determines that a“link reliability reduction event” has occurred and reports occurrenceof the link reliability reduction event to the eNB/cell/serving cell.

In the same manner, link reliability determination considering AoD (AoA)per Tx beam can be applied to the above-described examples.

Embodiment 4

Embodiment 4 of the present invention proposes a method of usingsub-condition enabling/disabling signaling in definition of RRM eventtrigger conditions using link reliability. According to this method, anadaptive technique for executing link reliability determination andhandover determination algorithms adaptively to situation can bedesigned in consideration of a UE movement speed, network state and thelike.

FIG. 16 illustrates a method of adjusting a link reliabilitydetermination algorithm and a handover determination algorithmadaptively to situation by enabling or disabling signaling per sub-tree.

In FIG. 16, an enabling/disabling signal may be information deliveredfrom an eNB/network/cell to a UE or control information generated by theUE according to a method defined per “case” when the currentcommunication situation is determined to correspond to a predefined“case” on the basis of the predefined “case”. In addition, although anembodiment of the present invention handles a case in which an RRM eventis defined by two parameters of Rx power and AoD (AoA) and a case inwhich two sub-conditions are defined, the sub-conditionenabling/disabling signal is applicable to a case in which three or moresub-conditions are defined in addition to the cases specified in thepresent invention.

FIG. 16 illustrates an enabling/disabling signal per sub-condition for acase in which a sub-condition is defined for each of three measurementparameters of Rx power, AoD and AoA, that is, three sub-conditions aredefined.

When the above-described proposed methods are applied, measurementduration may be differentially applied.

As another example of implementing the above-described proposal, amethod of performing measurement for different time durations forrespective parameters in consideration of time-varying characteristicsof the parameters with respect to channel characteristics may beconsidered when measurement is performed. That is, when the method asillustrated in FIG. 16 is applied, different measurement durations (ortime durations) are applied to respective parameters when whether a newRRM event is triggered is determined through three measurementparameters for link reliability determination, Rx, AoD and AoA, as anextension of the present invention.

In addition, when the above-described technique is applied, thefollowing RRM measurement values may be additionally fed back.

1. The number of rays/Tx beams equal to or higher than specific quality

2. Information about ray/Tx beam distribution, such as a maximumdifference and variance of AoD values of rays/Tx beams equal to orhigher than specific quality

3. The number of sub-arrays having a sufficient number of rays/Tx beamsequal to or higher than specific quality

FIG. 17 illustrates an apparatus for performing the above-describedoperations.

A radio apparatus 800 shown in FIG. 17 may correspond to theaforementioned UE installed in a specific vehicle as described above anda radio apparatus 850 may correspond to the aforementioned networkdevice (eNB/cell).

The UE may include a processor 810, a memory 820 and a transceiver 830and the eNB 850 may include a processor 860, a memory 870 and atransceiver 880. The transceivers 830 and 880 transmit/receive radiosignals and may be executed in the physical layer of 3GPP and the like.Particularly, the transceiver of the UE 800 in the vehicle may include aplurality of antenna sub-arrays and a central unit (CU) for controllingthe antenna sub-arrays for the aforementioned distributed antenna systemas illustrated in FIG. 2.

The processors 810 and 860 are executed in the physical layer and/or theMAC layer and are connected to the transceivers 830 and 880. Theprocessors 810 and 860 may perform the aforementioned UE mobilitymanagement method. In addition, the processor of the UE 800 in thevehicle may include the CU illustrated in FIG. 2 or control the CU.

The processors 810 and 860 and/or the transceivers 830 and 880 mayinclude a specific application-specific integrated circuit (ASIC),another chipset, a logic circuit and/or a data processor. The memories820 and 870 may include a ROM (Read-Only Memory), a RAM (Random AccessMemory), a flash memory, a memory card, a storage medium and/or anotherstorage unit. When an embodiment is executed by software, theaforementioned methods may be executed as modules (e.g., processors orfunctions) which execute the aforementioned functions. The modules maybe stored in the memories 820 and 870 and executed by the processors 810and 860. The memories 820 and 870 may be provided to the inside oroutside of the processors 810 and 860 or connected to the processors 810and 860 through a known means.

As described above, the detailed description of the preferredembodiments of the present invention has been given to enable thoseskilled in the art to implement and practice the invention. Although theinvention has been described with reference to exemplary embodiments,those skilled in the art will appreciate that various modifications andvariations can be made in the present invention without departing fromthe spirit or scope of the invention described in the appended claims.

INDUSTRIAL APPLICABILITY

As described above, the present invention is applicable to variouscommunication systems using a high-speed UE such as vehicularcommunication.

1-15. (canceled)
 16. A method of performing, by a user equipment (UE),reporting for mobility management in a wireless communication system,comprising: receiving signals transmitted from a network; determiningwhether a mobility related event of the UE has occurred through thesignals; and transmitting an event occurrence report to the network whenthe mobility related event of the UE has occurred, wherein whether themobility related event of the UE has occurred is determined inconsideration of receive (Rx) power of the signals and a raydistribution between the network and the UE.
 17. The method according toclaim 16, wherein the ray distribution between the network and the UE isconsidered using Angles of Departure (AoD) of the signals.
 18. Themethod according to claim 16, further comprising: determining linkreliability with a specific network device of the network isproportional to a number of propagating beams received from the specificnetwork device and magnitude of an AoD difference between thepropagating beams.
 19. The method according to claim 18, wherein thenumber of the propagating beams is counted except for the propagatingbeams having the Rx power smaller than a predetermined reference level.20. The method according to claim 16, wherein the Rx power of thesignals is considered through at least one of Rx power or quality of asignal received by each of a plurality of antenna units from eachnetwork device of the network, Rx power or quality of all signalsreceived by the plurality of the antenna units from each network deviceof the network, Rx power or quality of each preferred received signal ofeach of plurality of the antenna units from among signals received fromeach network device of the network, and Rx power or quality of allpreferred received signals of each of the plurality of the antenna unitsfrom among signals received from each network device of the network. 21.The method according to claim 16, wherein whether the mobility relatedevent of the UE has occurred is determined by setting differentmeasurement durations for respective parameters considered for whetherthe mobility related event of the UE has occurred.
 22. The methodaccording to claim 16, wherein whether the mobility related event of theUE has occurred is determined by independently determining whether aplurality of conditions is satisfied.
 23. The method according to claim16, wherein whether the mobility related event of the UE has occurred isdetermined by determining whether a second condition following the firstcondition is satisfied, when a first condition of the plurality ofconditions is satisfied.
 24. The method according to claim 16, whereinthe event occurrence report includes information about ray directivityfrom a specific network device of the network.
 25. A User Equipment (UE)for which mobility management is supported in a wireless communicationsystem, comprising: antenna units; and a central unit connected to theantenna units, wherein the antenna units are configured to receivesignals from a network, wherein the central unit is configured todetermine whether a mobility related event of the UE has occurredthrough the signals, and determine whether the mobility related event ofthe UE has occurred in consideration of receive (Rx) power of thesignals and a ray distribution between a network and the UE.
 26. The UEaccording to claim 25, wherein the central unit is further configured toconsider the ray distribution between the network and the UE usingAngles of Departure (AoD) of the signals.
 27. The UE according to claim25, wherein the central unit is further configured to determine linkreliability with a specific network device of the network isproportional to a number of propagating beams received from the specificnetwork device through the plurality of antenna units and an AoAdifference between the propagating beams.
 28. The UE according to claim27, wherein the number of the propagating beams is counted except forthe propagating beams having the Rx power smaller than a predeterminedreference level.
 29. The UE according to claim 25, wherein the Rx powerof the signals is considered through at least one of Rx power or qualityof a signal received by each of a plurality of antenna units from eachnetwork device of the network, Rx power or quality of all signalsreceived by the plurality of the antenna units from each network deviceof the network, Rx power or quality of each preferred received signal ofeach of plurality of the antenna units from among signals received fromeach network device of the network, and Rx power or quality of allpreferred received signals of each of the plurality of the antenna unitsfrom among signals received from each network device of the network. 30.The UE according to claim 25, wherein whether the mobility related eventof the UE has occurred is determined by setting different measurementdurations for respective parameters considered for whether the mobilityrelated event of the UE has occurred.